As technology of forming a full-color display using organic electroluminescence (“electroluminescence” and “electroluminescent” hereinafter may be abbreviated as “EL”), a three-color pattern formation method, a method of combining white EL with a color filter, a method of combining EL, a color conversion film, and a color filter, and the like have been known.
The three-color pattern formation method may achieve a high efficiency by adjusting the material balance and reducing the loss of a circular polarizer. On the other hand, since it is difficult to realize a high-definition display using the three-color pattern formation method due to difficulty in forming a three-color pattern, it is considered that a large-screen display cannot be formed.
The method of combining white EL with a color filter has a problem in which white EL emission efficiency is poor.
The method of combining EL with a color conversion film has a problem such as a poor red conversion efficiency, although various improvements have been made.
A full-color display method is divided into a bottom-emission structure and a top-emission structure. In the top-emission structure, light is outcoupled from the side opposite to the substrate, differing from a related-art structure in which light is outcoupled through a TFT glass substrate. This improves the aperture ratio with respect to the emitting part, whereby the luminance can be increased.
A method has been studied in which a semitransparent cathode is used as the upper electrode and only light having a specific wavelength is outcoupled from the EL device utilizing a multiple interference effect to achieve high color reproducibility. For example, an organic EL device has been disclosed in which a first electrode formed of a light reflecting material, an organic layer including an organic emitting layer, a semitransparent reflective layer and a second electrode formed of a transparent material are stacked so that the organic layer serves as a resonator and in which the following expression is satisfied when the peak wavelength of the spectrum of light to be outcoupled is λ (see patent document 1).(2L)/λ+Φ/(2π)=m Where L indicates the optical length, λ indicates the wavelength of light to be outcoupled, m indicates an integer, and Φ indicates the phase shift, configured so that the optical length L is the minimum positive value.
A display has also been disclosed in which each of R, G, and B pixels has a structure in which an organic EL layer is placed between a light reflective layer and a transparent layer and a color filter is disposed on the light-outcoupling side or the external light incident side of the transparent layer (see patent document 2).
[Patent document 1] WO01/39554
[Patent document 2] JP-A-2002-373776
However, the above EL device or display has the following problems.
(1) In order to form a full-color display, it is necessary to fabricate an EL device corresponding to each color. This requires that the EL device have a thickness corresponding to each color in pixel units, thereby making production difficult.
(2) The light selectivity may be insufficient since conditions where m in the above expression is small are utilized.
The invention was achieved in view of the above-described problems. An object of the invention is to provide an organic EL display which allows multicolor emission without decreasing the efficiency of the organic EL device and which is easily produced.
Through research for solving the foregoing subject, the inventors found that organic EL devices can emit light in different colors (multicolor emission) by adjusting optical thickness of a resonator in each device formed on the same substrate using an inorganic compound layer, and that an organic luminescent medium layer, light reflective layer, transparent electrode and the like can be each formed as a single common layer even in organic EL devices (pixels) emitting light in different colors without need of forming different layers in each device so that an organic EL display with high efficiency can easily fabricated. They completed the invention based on the findings.
The invention provides the following organic EL display and its production method.    1. An organic electroluminescent display comprising: a substrate; and a first organic electroluminescent device part and a second organic electroluminescent device part placed side by side on a surface of the substrate; the first organic electroluminescent device part including at least a light reflective conductive layer, an organic luminescent medium layer, and a transparent electrode layer in this order and including a light reflective layer inside or outside of the organic luminescent medium layer or the transparent electrode layer; the second organic electroluminescent device part including at least a light reflective conductive layer, a first inorganic compound layer, an organic luminescent medium layer, and a transparent electrode layer in this order and including a light reflective layer inside or outside of the organic luminescent medium layer or the transparent electrode layer; and an emission spectrum of light from the first organic electroluminescent device part differing from an emission spectrum of light from the second organic electroluminescent device part.    2. An organic electroluminescent display comprising: a substrate; and a first organic electroluminescent device part and a second organic electroluminescent device part placed side by side on a surface of the substrate; the first organic electroluminescent device part including at least a light reflective conductive layer, a first inorganic compound layer, an organic luminescent medium layer, and a transparent electrode layer in this order and including a light reflective layer inside or outside of the organic luminescent medium layer or the transparent electrode layer; the second organic electroluminescent device part including at least a light reflective conductive layer, a first inorganic compound layer, a second inorganic compound layer, an organic luminescent medium layer, and a transparent electrode layer in this order and including a light reflective layer inside or outside of the organic luminescent medium layer or the transparent electrode layer; and an emission spectrum of light from the first organic electroluminescent device part differing from an emission spectrum of light from the second organic electroluminescent device part.    3. An organic electroluminescent display comprising: a substrate; and a first organic electroluminescent device part, a second organic electroluminescent device part, and a third organic electroluminescent device part placed side by side on a single surface of the substrate; the first organic electroluminescent device part including at least a light reflective conductive layer, an organic luminescent medium layer, and a transparent electrode layer in this order and including a light reflective layer inside or outside of the organic luminescent medium layer or the transparent electrode layer; the second organic electroluminescent device part including at least a light reflective conductive layer, a first inorganic compound layer, an organic luminescent medium layer, and a transparent electrode layer in this order and including a light reflective layer inside or outside of the organic luminescent medium layer or the transparent electrode layer; the third organic electroluminescent device part including at least a light reflective conductive layer, a first inorganic compound layer, a second inorganic compound layer, an organic luminescent medium layer, and a transparent electrode layer in this order and including a light reflective layer inside or outside of the organic luminescent medium layer or the transparent electrode layer; and emission spectra of light from the first, second, and third organic electroluminescent device parts differing from one another.    4. The organic electroluminescent display according to any one of 1 to 3, wherein at least one of the first inorganic compound layer and the second inorganic compound layer is an inorganic compound layer subjected to crystallization treatment.    5. The organic electroluminescent display according to any one of 1 to 4, wherein at least one of the first inorganic compound layer and the second inorganic compound layer includes an inorganic oxide.    6. The organic electroluminescent display according to 4, wherein the first inorganic compound layer and the second inorganic compound layer include an inorganic oxide, and crystallinity of the first inorganic compound layer is higher than crystallinity of the second inorganic compound layer.    7. The organic electroluminescent display according to 6, wherein the first inorganic compound layer is crystalline, and the second inorganic compound layer is noncrystalline.    8. The organic electroluminescent display according to any one of 1 to 7, wherein at least one of the first inorganic compound layer and the second inorganic compound layer includes an oxide of an element selected from the group consisting of In, Sn, Zn, Ce, Sm, Pr, Nb, Tb, Cd, Ga, Al, Mo, and W.    9. The organic electroluminescent display according to any one of 1 to 7, wherein at least one of the first inorganic compound layer and the second inorganic compound layer includes an oxide of an element selected from the group consisting of In, Sn, and Zn.    10. The organic electroluminescent display according to any one of 1 to 9, wherein the light reflective conductive layer includes a metal selected from the group consisting of Al, Ag, Au, Pt, Cu, Mg, Cr, Mo, W, Ta, Nb, Li, Mn, Ca, Yb, Ti, Ir, Be, Hf, Eu, Sr, Ba, Cs, Na, and K, or an alloy containing at least one metal selected from the group.    11. The organic electroluminescent display according to any one of 1 to 10, wherein the light reflective layer includes one, or two or more metal elements selected from the group consisting of Al, Ag, Au, Pt, Cu, Mg, Cr, Mo, W, Ta, Nb, Li, Mn, Ca, Yb, Ti, Ir, Be, Hf, Eu, Sr, Ba, Cs, Na, and K.    12. The organic electroluminescent display according to any one of 1 to 11, further comprising a color conversion part.    13. The organic electroluminescent display according to any one of 1 to 12, further comprising a color filter.    14. The organic electroluminescent display according to 12, wherein the color conversion part is a fluorescence conversion film.    15. A method of producing the organic electroluminescent display according to any one of 1 to 14, the method comprising forming at least one of the first inorganic compound layer and the second inorganic compound layer by wet etching.
The organic EL display according to the invention allows multicolor emission without decreasing the luminous efficiency of the organic EL device by forming the organic EL devices having different resonators on a substrate.
Since the optical thickness of the optical resonator is controlled by forming the inorganic compound layer over the light reflective conductive layer, the optical thickness of each organic EL device part can be arbitrarily adjusted without changing the thickness of the organic luminescent medium layer optimally set for the emitting device.
Moreover, since the thickness of the organic luminescent medium layer and the like need not be adjusted in units of EL device parts which emit light of different colors, the organic EL display according to the invention can be easily produced.